The Holy Hop Drive was a device invented by Dr. Charles Holly. In theory, it enabled a starship to travel to any point in the universe instantly. It also allowed travel to any point in time, and, with arcane alterations, to alternate universes.
However the drive had a fatal design flaw. It was such a horrible violation of space/time and causality that any Holly Hop Drive is instantly spun off into it's own micro-verse, where the worst things that COULD happen to it do until it is destroyed. The universe simply won't tolerate the existence of the Holly Hop Drive.
The sole "operational" use of the Holly Hop drive was on the USS Harrier. This went weird and wrong from the start of the tests. And went weirder and wronger until Captain Jay P. Hailey destroyed the device. (Rumor has it that weird and wrong haunt the crew of the USS Harrier present on those tests.)
Charles Holly Did not do the research+ or he might have realized that the Mcmilllian Improbability Vectors completely neutralize his whole line of theorizing.
Upon belatedly realizing his drive was good solely for destruction and mayhem, Charles Holly somewhat urgently was retired to the Vulcan Science Academy where he pursues theoretical hyperspatial mathematics and is never allowed to build another dimension travel device.
+ WARNING: This link maliciously takes you to TV Tropes. Do not click unless you are willing to accept that an entire day's productivity is down the drain.